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Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration SystemGupta, Ankush 1986- 14 March 2013 (has links)
The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves.
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Dynamic modeling, optimization, and control of monoethanolamine scrubbing for CO2 captureZiaii Fashami, Sepideh 13 November 2012 (has links)
This work seeks to develop optimal dynamic and control strategies to operate post combustion CO2 capture in response to various dynamic operational scenarios. For this purpose, a rigorous dynamic model of absorption/stripping process using monothanolamine was created and then combined with a simplified steady state model of power cycle steam turbines and a multi-stage variable speed compressor in Aspen Custom Modeler. The dynamic characteristics and interactions were investigated for the plant using 30% wt monoethanolamine (MEA) to remove 90% of CO2 in the flue gas coming from a 100 MW coal-fired power plant.
Two load reduction scenarios were simulated: power plant load reduction and reboiler load reduction. An ACM® optimization tool was implemented to minimize total lost work at the final steady state condition by adjusting compressor speed and solvent circulation rate. Stripper pressure was allowed to vary. Compressor surge limit, run off condition in rich and lean pumps, and maximum allowable compressor speed were found as constraints influencing the operation at reduced loads. A variable speed compressor is advantageous during partial load operations because of its flexibility for handling compressor surge and allowing the stripper and reboiler to run at optimal conditions. Optimization at low load levels demonstrated that the most energy efficient strategy to control compressor surge is gas recycling which is commonly applied by an anti-surge control system installed on compressors. Trade offs were found between initial capital cost and optimal operation with minimal energy use for large load reduction. The examples are, designing the stripper in a way that can tolerate the pressure two times larger than normal operating pressure, over sizing the pumps and over designing the compressor speed.
A plant-wide control procedure was used to design an effective multi-loop control system. Five control configurations were simulated and compared in response to large load variations and foaming in the stripper and the absorber. The most successful control structure was controlling solvent rate, reboiler temperature, and stripper pressure by liquid valve, steam valve, and compressor speed respectively. With the investigated disturbances and employing this control scheme, development of an advanced multivariable control system is not required. This scheme is able to bring the plant to the targeted set points in about 6 minutes for such a system designed initially with 11 min total liquid holdup time.Frequency analysis used for evaluation of lean and rich tanks on the dynamic performances has shown that increasing the holdup time is not always helpful to damp the oscillations and rejecting the disturbances. It means there exists an optimum initial residence time in the tanks. Based on the results, a 5-minute holdup can be a reasonable number to fulfill the targets. / text
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An experimental and simulation based approach toward understanding the effects of obesity on balance recovery from a postural perturbationMatrangola, Sara Louise 17 October 2011 (has links)
Obesity is associated with an increased risk of falls and subsequent injury. Most falls result from some type of postural perturbation. As such, it is important to understand how obesity influences balance recovery from a postural perturbation. There is limited information on the effects of obesity on balance recovery, and the limited available information is ambiguous. Therefore, the purpose of the research within this dissertation was to investigate the effects of obesity on balance recovery after a postural perturbation in young adults to better understand how obesity contributes to fall risk.
Four separate studies make up this dissertation. The purpose of the first study was to investigate the effects of obesity on balance recovery ability using an ankle strategy in young adults. Normal-weight and obese participants recovered balance using an ankle strategy after three types of postural perturbations: an initial angular displacement, an initial angular velocity from the natural stance, and an initial angular velocity from a prescribed position. Obese participants were unable to recover balance using an ankle strategy as well as normal-weight participants when perturbations involved an initial angular velocity. However, no differences between obese and normal-weight participants were found when perturbations only involved an initial angular displacement. The effect of obesity on balance recovery in young adults was dependent on the perturbation characteristics, and may be explained by a possible beneficial effect of increased inertia on balance recovery after perturbations with little or no initial angular velocity.
The purpose of the second study was to examine the effects of obesity on balance recovery by stepping in young adults. The ankle strategy has the benefit of simplifying the mechanics of balance recovery, but limits generalizability to more realistic fall scenarios where stepping to extend the base of support and recover balance is desired. Similar to the first study, participants attempted to recover balance following two types of postural perturbations: an initial angular displacement from an upright stance (by releasing participants from a static forward lean), and an initial angular velocity while in an upright stance (using a translating platform). In contrast to the first study, the ability to recover balance with a single-step did not differ between young normal-weight and obese adults. These results suggest that the reported increase in fall risk in obese adults is not a result of impaired balance recovery ability (at least among young adults that were tested here).
The third study examined the effects of obesity on body kinematics immediately following a trip-like perturbation in young adults. Obesity was found to increase body angular velocity the perturbation, and that increases in body angular velocity were associated with an increased probability of a failed recovery. These results suggest that when a young obese and young normal-weight individual trip while walking at similar speeds, the young obese individual may be at a greater risk of falling following a trip because the young obese individual will experience a greater body angular velocity. This detrimental effect of obesity on the difficulty of recovering from a trip-like perturbation in young adults is most likely due to how mass is distributed throughout the body and not the amount of mass itself.
The final study examined the relationship between relative strength and functional capability in young adults, and how obesity influences this relationship. To compare relative strength used during a functional task (i.e. balance recovery from a forward fall), the obese and normal-weight individual should complete the task with identical kinematics. Forward dynamic simulations were used to address this research question, instead of human subjects testing, to achieve identical kinematics. Differences in peak relative torques were found between the normal-weight and obese model, with the largest differences seen at the hip. These findings suggest that young obese individuals use greater relative strength at some joints than young normal-weight individuals to perform the time-critical task of balance recovery, and that these differences in relative strength demands may limit functional capability in young individuals who are obese. / Ph. D.
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Design and Simulation of a Towed Underwater VehicleLinklater, Amy Catherine 07 July 2005 (has links)
Oceanographers are currently investigating small-scale ocean turbulence to understand how to better model the ocean. To measure ocean turbulence, one must measure fluid velocity with great precision. The three components of velocity can be used to compute the turbulent kinetic energy dissipation rate. Fluid velocity can be measured using a five-beam acoustic Doppler current profiler (VADCP). The VADCP needs to maintain a tilt-free attitude so the turbulent kinetic energy dissipation rate can be accurately computed to observe small-scale ocean turbulence in a vertical column.
To provide attitude stability, the sensor may be towed behind a research vessel, with a depressor fixed somewhere along the length of the towing cable. This type of setup is known as a two-part towing arrangement.
This thesis examines the dynamics, stability and control of the two-part tow. A Simulink simulation that models the towfish dynamics was implemented. Through this Simulink simulation a parametric study was conducted to see the effects of sea state, towing speed, center of gravity position, and a PID controller on the towfish dynamics. A detailed static analysis of the towing cable's effects on the towfish enhanced this dynamic model. The thesis also describes vehicle design and fabrication, including procedures for trimming and ballasting the towfish. / Master of Science
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DYNAMIC MODELING AND CONTROL OF REACTIVE DISTILLATION FOR HYDROGENATION OF BENZENEAluko, Obanifemi 16 January 2010 (has links)
This work presents a modeling and control study of a reactive distillation column
used for hydrogenation of benzene. A steady state and a dynamic model have been
developed to investigate control structures for the column. The most important aspects of
this control problem are that the purity of the product streams regarding benzene need to
be met. At the same time as little toluene as possible should be converted. The former is a
constraint imposed by EPA regulations while the latter is tied to process economics due
to the high octane number of toluene. It is required to satisfy both of these objectives
even under the influence of disturbances, as the feed composition changes on a regular
basis. The dynamic model is used for developing transfer function models of two
potential control structures. Pairing of inputs and outputs is performed based upon the
Relative Gain Array (RGA) and PI controllers were designed for each control structure.
The controller performance was then compared in simulation studies. From our results,
control structure 2 performed better than control structure 1. The main advantage of CS2
over CS1 is noticed in the simulation of feed composition disturbance rejection, where
CS2 returns all variables back to steady state within 3 hrs while it take CS1 more than 20
hrs to return the temperature variables back to steady state.
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A System Dynamic Study in Steel Industry for the Strategy of CO2 MitigationChen, Chun-Da 29 June 2007 (has links)
The development of steel industry makes progress simultaneously with economy and society of a country. The steel industry is an important industry for each country. From 2001, there was an insufficient supply gap of steel due to strong demand of China, which pushes main integrated steel works to increase their capacities. However, the mitigation pressure of the emission of Green House Gas make a limitations for capacity expansion. The objective of this study is to make appropriate policies for integrated steel works to cope with new operation environment.
From the analysis of steel industry, this study discovers the features and the related operation issues of global steel industry. The relationship between production and CO2 emission was investigated, and the casual loop among the production, revenue, and CO2 emission was analyzed. A dynamic model was developed by system dynamics approach and related tools to simulate the dynamic relationship between the revenue and CO2 emission of steel work. After thorough tests of reliability, model behavior, and policy implications, this model was used to investigate the influence of main operational and environmental parameters on the revenue of steel work. The appropriate production policies for steel works was also proposed.
Simulation results showed that, there was no universal production policy without the economic penalty for CO2 emission, but keeping the production under regulation limit was the most suitable strategy after the implementation of economic penalty. Increasing energy utilization efficiency, the ration of R&D budget in annual profit, and lowering the growth rate of production would facilitate the revenue increase of steel work. The simultaneous adjustment of these parameters could downgrade the negative effect of economic penalty.
The main strategy to cope with the pressure of the CO2 mitigation is to reduce the unit cost of mitigation. Four approaches can be adopted by the steel work to tackle the CO2 mitigation. They are (1) carefully scheduling the capacity expansion of steel work, (2) actively deriving the legislation of economic penalty for CO2 emission, (3) reducing the unit cost for CO2 mitigation, (4) enhancing the power of R&D activities.
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Dynamic Modeling and Control of Distributed Heat Transfer Mechanisms: Application to a Membrane Distillation ModuleEleiwi, Fadi 12 1900 (has links)
Sustainable desalination technologies are the smart solution for producing fresh water
and preserve the environment and energy by using sustainable renewable energy
sources. Membrane distillation (MD) is an emerging technology which can be driven
by renewable energy. It is an innovative method for desalinating seawater and brackish
water with high quality production, and the gratitude is to its interesting potentials.
MD includes a transfer of water vapor from a feed solution to a permeate
solution through a micro-porous hydrophobic membrane, rejecting other non-volatile
constituents present in the influent water. The process is driven by the temperature
difference along the membrane boundaries. Different control applications and
supervision techniques would improve the performance and the efficiency of the MD
process, however controlling the MD process requires comprehensive mathematical
model for the distributed heat transfer mechanisms inside the process. Our objective
is to propose a dynamic mathematical model that accounts for the time evolution of
the involved heat transfer mechanisms in the process, and to be capable of hosting
intermittent energy supplies, besides managing the production rate of the process,
and optimizing its energy consumption. Therefore, we propose the 2D Advection-Diffusion Equation model to account for the heat diffusion and the heat convection mechanisms inside the process. Furthermore, experimental validations have proved
high agreement between model simulations and experiments with less than 5% relative
error. Enhancing the MD production is an anticipated goal, therefore, two main
control strategies are proposed. Consequently, we propose a nonlinear controller for
a semi-discretized version of the dynamic model to achieve an asymptotic tracking
for a desired temperature difference. Similarly, an observer-based feedback control
is used to track sufficient temperature difference for better productivity. The second
control strategy seeks for optimizing the trade-o between the maximum permeate flux production for a given set of inlet temperatures of the feed and the permeate solutions,
and the minimum of the energy consumed by the pump
ow rates of the feed
and the permeate solutions. Accordingly, Extremum Seeking Control is proposed for
this optimization, where the pump
flow rates of the feed and the permeate solutions
are the manipulated control input.
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Reduced Order Modeling for Vapor Compression Systems via Proper Orthogonal DecompositionJiacheng Ma (8072936) 04 December 2019 (has links)
<p>Dynamic
modeling of Vapor Compression Cycles (VCC) is particularly important for
designing and evaluating controls and fault detection and diagnosis (FDD)
algorithms. As a result, transient modeling of VCCs has become an active area
of research over the past two decades. Although a number of tools have been
developed, the computational requirements for dynamic VCC simulations are still
significant. A computationally efficient but accurate modeling approach is
critically important to accelerate the design and assessment of control and FDD
algorithms where a number of iterations with a variety of test input signals
are required. Typically, the dynamics of compressors and expansion devices
evolve on an order of magnitude faster than those of heat exchangers (HX)
within VCC systems. As a result, most dynamic modeling efforts have focused on
heat exchanger models. The switched moving boundary (SMB) method, which
segments a heat exchanger depending on thermodynamic phase of the refrigerant,
i.e. subcooled liquid, two-phase and superheated vapor, and moves control
volumes as the length of each phase changes, can reduce the computation time
compared with the finite volume (FV) method by solving fewer equations due to a
smaller set of control volumes. Despite the computational benefit of the SMB,
there is a well-known numerical issue associated with switching the model
representations when a phase zone disappears or reappears inside of a heat
exchanger. More importantly, the computational load is still challenging for many
practical VCC systems. This thesis proposes an approach applying nonlinear
model order reduction (MOR) methods to dynamic heat exchanger models to
generate reduced order HX models, and then to couple them to quasi-static
models of other VCC components to complete a reduced order VCC model. To enable
the use of nonlinear model reduction techniques, a reformulated FV model is
developed for matching the baseline MOR model structure, by using different
pairs of thermodynamic states with some appropriate assumptions. Then a
rigorous nonlinear model order reduction framework based on Proper Orthogonal
Decomposition (POD) and the Discrete Empirical Interpolation Method (DEIM) is
developed to generate reduced order HX models. </p><p>
</p><p> The proposed reduced order modeling approach
is implemented within a complete VCC model. Reduced order HX models are
constructed for a centrifugal chiller test-stand at Herrick Labs, Purdue
University, and are integrated with quasi-static models of compressor and
expansion valve to form the complete cycle. The reduced cycle model is
simulated in the Modelica-based platform to predict load-change transients, and
is compared with measurements. The validation results indicate that the reduced
order model executes 200 times faster than real time with negligible prediction
errors.</p><br>
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Enantioselective nanofiltration using predictive process modeling: bridging the gap between materials development and process requirementsBeke, Aron K. 10 1900 (has links)
Organic solvent nanofiltration (OSN) is a low-energy alternative for continuous separations in the chemical industry. As the pharmaceutical sector increasingly turns toward continuous manufacturing, OSN could become a sustainable solution for chiral separations. Here we present the first comprehensive theoretical assessment of enantioselective OSN processes. Lumped dynamic models were developed for various system configurations, including structurally diverse nanofiltration cascades and single-stage separations with side-stream recycling and in situ racemization. Enantiomer excess and recovery characteristics of the different processes were assessed in terms of the solute rejection values of the enantiomer pairs. The general feasibility of stereochemical resolution using OSN processes is discussed in detail. Fundamental connections between rejection selectivity, permeance selectivity, and enantiomer excess limitations are revealed. Quantitative process performance examples are presented based on theoretical rejection scenarios and cases from the literature on chiral membranes. A model-based prediction tool can be found on www.osndatabase.com to aid researchers in connecting materials development results with early-stage process performance assessments.
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Dynamics of Affordance ActualizationNordbeck, Patric C. January 2017 (has links)
No description available.
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